1. Segmented Worms
Section 27.2

2. Animal Classification
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Enchinoderms
- Phylum Platyhelimenthes
- Phylum Nematoda
- Phylum Annelida
Worms
Invertebrates
Animals
Fishes
Amphibians
Reptiles
Ectotherms
(cold-blooded)
Vertebrates
Birds
Mammals
Endotherms
(warm-blooded)

3. Segmented Worms Phylum Annelida Coelomates with two body openings
Latin term anellus = “little ring"
Examples: Earthworms, bristleworms, and leeches
Coelomates with two body openings

4. Segmented Worms
Can be found in most environments, except in frozen soil and dry, compact sand
15,000 species of segmented worms
Earthworm
Bristleworm
Leech

5. External Anatomy of an Earthworm
Prostomium – a tongue-like lobe above the mouth
Clitellum - the swelling of the earthworm near its anterior side
Setae - Tiny bristles that help earthworms and bristleworms move through soil
Mouth
Anus

7. Nervous System Segmented worms have simple nervous systems
Some species have eyes and brains
All species have nerve cords and ganglia

8. Internal view of an earthworm

9. Circulatory
Segmented worms have a closed circulatory system – blood flows through vessels to reach all parts of the body
Open circulatory system – blood is not enclosed in vessels throughout the entire body
Examples: flatworms and roundworms

10. Internal view of an earthworm

11. Respiration
Segmented worms must live in water or wet areas because they are able to exchange gases directly through their moist skin

12. Digestion Annelids have a complete digestive system
Have a crop and a gizzard
Crop – a sac that holds soil temporarily before it moves into the gizzard
Gizzard – a muscular organ that grinds food

13. Internal view of an earthworm

14. Excretion
Annelids have two nephridia in almost every segment that collect waste products and transport them out of the body

15. Internal view of an earthworm

16. Reproduction Earthworms and leeches are hermaphrodites
During sexual reproduction, worms exchange sperm
Eggs are fertilized and laid in the soil
The eggs hatch in 2-3 weeks
Bristleworms have separate sexes and reproduces sexually

17. Internal view of an earthworm

18. Leeches
Many species are parasites that suck blood or other body fluids from their hosts
Front and rear suckers enable leeches to attach themselves to their hosts

19. Leeches The saliva contains chemicals that act as a anesthetic
Example – Novocain
Other chemicals prevent the blood from clotting
Leeches are used medically to remove decaying tissues of patients

20. Leeches A leech can ingest 2-5 times its own weight in one meal
A leech will drop off its host when its full and may not eat again for months